1. Field of the Invention
The invention relates to a method for producing a vacuum between two sheets of glass and insulating glazing thus produced.
The method according to the invention, although it is not limited to the production of insulating glazing, will be described more particularly by reference to this application.
2. Discussion of the Background
It is usual, in order to obtain thermal and/or acoustic insulation, to produce insulating glazing including two sheets of glass separated from one another by a relatively thick air gap. Such glazing provides thermal insulation which is judged to be insufficient for certain occasions. To remedy that, it is known to produce glazing including three sheets of glass and one of the air gaps can be replaced by a gas, for example krypton. This glazing has markedly enhanced thermal insulation properties, but is so thick that it is not always easy to use it.
Moreover, current demand from the users is turning towards thermal insulation of glazing equivalent to that of solid walls. Insulating glazing had already been proposed, particularly in Patent No. WO-91/02878, consisting of two sheets of glass separated from one another by a space in which a vacuum has been produced.
This glazing, due to the vacuum, achieves very good insulation but it is very difficult to produce. On the one hand, the slight thickness between the two sheets of glass, which is of tenths of a millimeter, has to be constant over the whole region where the sheets of glass are face-to-face.
Moreover, a perfectly leaktight seal has to be formed between the two sheets of glass.
Patent No. WO-91/02878 describes a technique consisting in placing studs a few tenths of a millimeter thick on one of the sheets of glass, which are distributed over the whole surface, and, at the same time, a joint which will allow the two sheets of glass to be sealed. These studs and this seal are produced in the same material, which is a glass-making composition. It is apparent that this glazing is difficult to produce due to these simultaneous operations which require intricate handling.
Moreover, the sealing joint has a number of bubbles which can impair the leaktightness and the aesthetics.
This patent also describes a method for forming the vacuum between the two sheets of glass. It particularly proposes inserting a tube between the two sheets of glass before sealing, to which a connection is made in order to pump out the air. Another embodiment consists in piercing a hole through one of the sheets of glass and in pumping out the air through this orifice.
In the first case, it is necessary to seal the tube in a leaktight fashion at the same time as the sheets of glass, which makes the operations difficult. Moreover, it is necessary, after having formed the vacuum, to seal the end of the tube, then to protect this end in order to avoid breaking.
In the second case, the vacuum is formed by means of a tube previously sealed around the hole. Then, after having formed the vacuum, this tube is melted so as to seal its end. The disadvantage of these embodiments is that the insulating glazing provided has a fragile point either on the periphery or on one surface. In the second case, part of the tube remains outside the glazing, which increases the risks of damage.
The object of the invention is a method for producing a vacuum between two sheets of glass, which is simple to produce, with the glazing produced advantageously having no fragile point.
This object is achieved according to the invention by a method for producing a vacuum between two sheets of glass capable, in particular, of constituting insulating glazing, one of the sheets of glass including a hole pierced through its thickness, consisting, after having deposited spacers between the two sheets of glass, in forming a sealing joint at the periphery of the sheets of glass, in forming the vacuum and in stopping the hole, the spacers being fixed on to a sheet of glass by bonding with an inorganic compound covering at least the bonding areas on the sheet of glass, the second sheet of glass being deposited on the spacers and on the peripheral sealing joint, and bonding with the inorganic compound being carried out simultaneously with the peripheral sealing.
According to a first embodiment, the inorganic compound is sodium silicate in aqueous solutions. This compound advantageously coats the spacers and is dried before they are deposited on the sheet of glass. This drying allows easy handling of the spacers. Bonding of the spacers to the sheet of glass is achieved by remoistening the inorganic compound, then drying them.
According to another embodiment, the inorganic compound is an enamel.
In particular, this second embodiment according to the invention is, on the one hand, simplified because the second sheet of glass can simply come to rest on the spacers which are integral with the first sheet of glass. This technique allows precise depositing of the second sheet of glass, which is less strict than according to the known techniques, the deposition being able to be slightly corrected, for example by sliding. Moreover, at this stage of the method, the enamel has not yet been fired, but the usual enamel pastes exhibit sufficient viscosity to hold the spacers in place, more particularly after the enamel paste has dried, during the phase of putting in place and positioning the sheet of glass. Moreover, a variant can provide for the sealing joint advantageously to be put in place after the second sheet of glass, still in order to facilitate the positioning thereof.
Moreover, the method makes provision to carry out the sealing and the firing of the bonding enamel simultaneously, which limits the number of stages of the method. For preference, the bonding enamel is identical to the sealing joint; otherwise the firing temperatures are advantageously chosen to be similar.
According to a first embodiment of the invention, the bonding of the spacers is carried out by successive depositions of dots of inorganic bonding compound, for example by screen printing, then depositions of the spacers by a suction tool pierced with holes which are smaller than the spacers, at the same pitch as the dots obtained.
The dots of inorganic bonding compound can be deposited by any type of device known to a person skilled in the art, making it possible to form dots with a diameter of the order of 0.5 mm and with a thickness of a few tens of microns and to arrange them very precisely with a regular pitch. Such a pitch particularly allows a number of dots lying advantageously between 600 and 1500 per square meter, and preferably equal to 1000 per square meter.
For preference, the suction tool picks up and transports the spacers previously arranged on a plate and deposits them on the dots of inorganic compound by stopping the suction and possibly by blowing.
The spacers according to the invention advantageously have a parallel-face, bi-truncated spherical shape. Such a shape makes it possible to place all the spacers on a plate in the same position, for example by causing the plate to vibrate; this occurs because the bulging part of the spacers has a tendency to bring them on to one of the parallel faces. Moreover, the previously described shape associated with the suction tool allows good gripping of the spacers and precise deposition thereof, one of the flat faces ensuring good stability, including before firing the bonding enamel. Such spacers advantageously have a distance between the parallel faces of between 0.1 and 0.3 millimeter and a diameter, in the region of the bulging part, of less than 0.5 millimeters.
According to a second embodiment of the method according to the invention, the bonding of the spacers is carried out by depositing the spacers on the surface of a sheet of glass, said spacers previously being covered, over the area coming into contact with the glass, with the inorganic bonding compound.
For preference, the spacers are transported by a suction tool which, during transport, moistens the relevant area of the spacers with a composition of the inorganic bonding compound, then they are deposited on the glass, having already been covered with the inorganic bonding compound on the desired area.
Concerning the sealing phase, during which the bonding of the spacers is simultaneously carried out, the method according to the invention advantageously makes provision to exert pressure between the two sheets of glass. Such pressure ensures that the sealing joint is brought to the same height as the spacers. This occurs because the sealing joint is initially deposited with a thickness greater than that of the spacers and is thus brought back to the desired thickness by squeezing.
Concerning the stopping of the hole provided in the thickness of one of the sheets of glass in order to form the vacuum, the invention provides for the stopper to be held close to the hole so as to let the air pass through, and which can be soldered to the glass. Such a stopper is advantageously produced from glass or metal. The link between the stopper and the sheet of glass is preferably obtained by inorganic welding, such as an enamel or sintered glass, the melt point of which is less than that of the glass and of the stopper. According to a preferred embodiment, before the vacuum-forming stage, a ring of silver-based enamel is deposited around the hole, and after firing, the ring is tinned and finally partially welded to a tinned inorganic disc. Firing of the silver enamel is advantageously carried out either simultaneously with that of the bonding enamel, or during a thermal toughening stage if such a stage is carried out.
Such an embodiment makes it possible to arrange, close to the hole, the disc intended to stop it, while keeping the hole open and allowing the vacuum to be produced for example by the use of a bell housing arranged around the hole.
According to this configuration, in the course of the vacuum-forming phase, the temperature is raised locally around the hole until the tin melts. Thus, the disc is soldered on to the sheet of glass and the hole is stopped, the vacuum being formed between the two sheets of glass.
Assembling the two sheets of glass between which the vacuum has been formed is simple to carry out. Moreover, the stopping of the hole through which the vacuum is formed does not constitute a fragile point and is relatively discreet; the excess thickness obtained in the region of the hole can be less than 1 mm.
According to a variant of the invention, a tinned metal ring is fastened to the glass by a solder glass replacing the silver-based enamel. This variant leads to a slightly greater excess thickness.
The techniques for stopping the hole which have just been described are entirely suitable for the technique of assembling the previously described sheets of glass, and more particularly for the choice and the fitting of the spacers as well as for the peripheral sealing; however, the invention does not exclude the possibility of combining the technique for stopping a hole in order to create a vacuum with other types of assembly.
The invention also proposes insulating vacuum glazing particularly capable of being produced according to the previously described method.
According to the invention, the insulating vacuum glazing consists of two sheets of glass held apart from one another by spacers and a peripheral sealing joint, said spacers being parallel-faced bi-truncated spheres made of ceramic. The sheets have advantageously undergone toughening treatment in order to reinforce their mechanical properties. For preference, this is a heat treatment toughening which leads to compression stresses over a relatively substantial thickness. The spacers are produced, for example, from a crystalline phase of zircons in a vitreous phase of silica.
According to a preferred embodiment of the invention, the parallel-faced bi-truncated spheres are obtained from balls coated in a material which can be poured and which can easily be separated from the spacers subsequently, for example by thermal and/or chemical and/or mechanical action. Such a material is, for example, tin, a metal alloy, an organic binder, a binder such as plaster, etc. The balls are coated in the material so as to form a single layer, said layer being eroded on its two faces. The balls used are, for example, balls usually used for cleaning glass-making moulds by sand blasting.
Also preferably, the sealing joint is an enamel, the firing temperature of which is less than 450xc2x0 C. The temperature reached must not, in particular, cause the stresses obtained by toughening to be relaxed.
The glazing according to the invention may also include, on its outer surface, an inorganic disc or pellet soldered to the glass. As previously described, such a disc is used to stop the hole which served to form the vacuum. This disc is preferably placed on the edge of the glazing for reasons of discreetness and particularly so as to be masked by the mounting devices.
The soldering of the disc is advantageously carried out using tin, and contact with the glass takes place via a layer of silver-based enamel.
According to other advantageous embodiments, the invention makes provision for using at least one sheet of glass covered with one or more functional layers, on at least one of its faces. Such layers are, for example, low-emissive layers as described in the French Patent No. 2,701,474. In the case in which a layer of this type is produced on the inner face of the glazing, that is to say a face subsequently in contact with the vacuum, the invention preferably makes provision for the layer to be removed over the peripheral area of the surface corresponding to the area covered by the sealing joint; this removal may allow better adhesion of the joint.